1. Field of the Invention
This invention relates to comminution apparatus, and in particular to tub grinders of the type having a receptacle defined by a stationary angled floor and a rotating cylindrical wall. The wall is positioned adjacent to the floor with its axis at right angle to the floor and at a substantial angle away from the vertical. An aperture in the floor leads to a hammer mill or other comminution means.
2. Description of the Prior Art
Tub grinders are well known, and are commonly used in applications such as comminuting yard waste, branches, shrubs, stumps, logs, forage crops, wooden pallets, railroad ties, slabwood, paper, cardboard, and many other materials. In such grinders, a hammer mill or other comminution means is located beneath a receptacle, with the hammers rotating about a horizontal axis with the hammers projecting up slightly into the receptacle, through an aperture provided in the stationary bottom of the receptacle. Rotating the wall of the receptacle feeds the material past the area of the hammers. The hammers pull the material through a cylindrical housing, pulverizing it and then shooting it out an exhaust, usually via a simple discharge chute.
The receptacles may be mounted with their main axis vertically oriented, in which case they are commonly referred to as tub grinders, or with the main axis at a substantial angle away from the vertical, in which case they may be referred to as tumble grinders.
Although hammer mills are commonly used in such grinders, other comminution apparatus is also common, such as flails or grinding rollers.
In any tub or tumble grinder, much of the debris being dumped into the receptacle for processing may already be sufficiently small to not require further comminution. In the case of yard waste, for example, the debris may include a large volume of abrasive aggregate including earth, sand, small stones and other abrasive materials which significantly reduce the life of the hammers or other wearing components of the comminution apparatus.
Also, it is frequently desirable to regrind material which has already been through the tumble grinder once. Naturally, a substantial portion of such reprocessed material has already been reduced to a desirable size. However, once debris is dumped into the receptacle, all of it must exit through the hammer mill or other comminution apparatus.
Thus, in a conventional grinder, it is common to process much more material through the hammer mill or other comminution apparatus than may really be necessary. This is certainly not a desirable characteristic, since it reduces the rate at which material may be processed, and places unnecessary wear on the hammers or other comminution means.